Rotary anode plate for X-ray tubes



Aug. 13, 1968 A. F. ELSAS 3,397,338

ROTARY ANODE PLATE FOR X-RAY TUBES Filed Feb. 25, 1965 11 70 7 /Z 12 Q I8 J5ZZ/67Zf0r. Jd0/f/?[5@5.

llnited States Patent 3,397,338 ROTARY ANODE PLATE FOR X-RAY TUBES AdolfFriedrich Elsas, Erlangen, Germany, assignor to SiemensAktiengesellschaft, Erlangen, Germany, a corporation of Germany FiledFeb. 25, 1965, Ser. No. 435,178

' 3 Claims. (Cl. 313-330) ABSTRACT OF THE DISCLOSURE A rotary anodeplate for X-ray tubes in which at least the electron impact surface isformed of a high melting alloy which consists of tungsten, osmium, andanother high melting metal, such as rhenium.

The invention is concerned with a rotary anode plate for X-ray tubes inwhich, at least, the electron impact surface consists of an alloy ofrefractory metals.

It was found that when rotary anode plates of tungsten are used, theelectron impact surface is gradually roughened owing to the load towhich the tube is subjected while radiation is generated and that theroughening of the impact surface reduces the radiation output. Theroughening of the impact surface was largely reduced by providing theelectron impact surface with rhenium and its alloys which are softer andmore ductile than tungsten. However, rhenium is very expensive so thatits use in sufiicient quantities proves prohibitive for reasons ofeconomy. Consequently rhenium is being used as an alloy with tungstenand with a rhenium content of 1 up to 35% adequate alloys were obtained.Moreover, 5 up to 25% of the tungsten content of these alloys werereplaced by high-melting metals such as niobium or tantalum. Suchalloys, however, still prove to be relatively expensive. Hence, it wasdecided to apply them by layers which form at least the anode platesurface hit by the electrons. Anode plates provided with a layer whichcontains rhenium still turned out to be rather expensive.

According to the invention a reduction of costs for anode plates inwhich at least the electron impact surface is formed by an alloy ofhigh-melting ;metals was obtained by using an alloy of tungsten-osmiumcontaining at least a tungsten content of 65%, an osmium content of upto approximately, and a content of 0 up to 25% of one or severalhigh-melting metals.

Starting from the known finding that with tungsten alloys containingadditives to increase ductility a portion of up to 25% of the tungstencontent can be replaced by one or several other high-melting metals andthat in accordance with the invention the osmium content shall amount toabout 10%, a tungsten content of up to 65% is attained.

By using a tungsten-osmium alloy a metal of greater hardness is producedas compared with tungsten-rhenium alloys. According to the opinion onthe effect of the tungsten-rhenium alloy an impairment of the anodeplate would develop when osmium is used as alloy ingredient. Moreover,an unfavourable reduction of the usability of the alloy would be broughtabout because of the lower melting point of osmium as compared withrhenium. However, it is surprising to see that already 1% of osmiumsuflices to obtain the effect which is achieved by adding 5 to 10%rhenium. For instance, a tube whose anode plate is provided with anelectron impact surface made of a tungsten-osmium alloy, osmiumaccounting for 1%, shows after 10,000 loadings a decrease of theradiation output which is also found in tubes whose electron impactsurface is formed by a rhenium-tungsten alloy, the rhenium contentaccounting for 10%. A cost reduction is obtained for the anode platesmade in accordance with 3,397,338 Patented Aug. 13, 1968 the inventionby the possibility of lessening by factor 5 to 10 the quantity of osmiumrequired for the improvement and the alloy without experiencing animpairment of the properties. The osmium content can be limited to 10%because this percentage allows the desired improvement to be obtained tosuch an extent that increasing the osmium content would no longer proverewarding economically. Apart from this, if the osmium content isincreased considerably in excess of 10%, this would lower the meltingpoint and the heat conductivity, two factors tending to lessen the tuberating. When the limit of 10% of the osmium content is exceededslightly, this would still fall within the scope of the invention.

Also with tungsten-rhenium alloys an addition of osmium proves to beadvantageous. Such alloys may have a composition with tungsten accouning for with osmium accounting up to about 10%, and with a portion ofother metals, let us say rhenium, ranging from 0 to about 10%. An osmiumcontent of 1% can also replace the elfect of 5 up to 10% rhenium. Whenthe rhenium content ranges from 1 to 10%, the additional osmium portionmay amount to 0.1 up to about 10%. As mentioned in the foregoingexample, even in this case the costs of the tube can be reduced becausea substantial quantity of the more expensive rhenium content is replacedby a small portion of osmium.

Moreover it proves to be of advantage that because of the smallerquantity of the required osmium content and the resulting cost reductionof the material the whole anode is made of the alloyed material. In thismanner the necessity of applying a compound layer is eliminated.

When the osmium alloy covered by the invention is used in a so-calledcompound anode, a surface layer, usually 0.1 to 2 mm. thick, is appliedto a base of tungsten or molybdenum or an alloy of these metals. Hereagain the share of expensive additives is smaller than with known tubesso that a reduction of cost is ensured.

The illustration shows an example of a rotary anode tube 1 embodying theinventive idea and representing a sectional view with a cut-awayenvelope and rotary anode plate. The glass envelope 2 embraces cathode 3fitted at one envelope end with leads 4 and the rotary anode 5 fitted atthe other end. Both envelopes 2 and cathode 3 as well as rotary anode 5,consisting of rotor 6 and anode plate 7, are arranged and supported in aknown manner. Plate 7 is provided with carrier 8 made of molybdenum andtungsten alloy which contains 5% tungsten and molybdenum and theunavoidable impurities. Electron impact surfaces 10 and 11, which aredifferently inclined with respect to plate spindle 9, are formed of an 1mm. thick layer 12 of tungsten alloy with osmium accounting for 1%. Inorder to obtain, in accordance with the inventive idea, an improvedloadability, it is also possible to provide stationary anodes of X-raytubes with an impact surface containing osmium.

I claim:

1. An X-ray tube, having an anode body with an exposed electron impactsurface, and electron beam means for producing an electron beamimpinging on said surface and causing emission of X-rays therefrom;

said electron impact surface consisting of a tungstenosrnium alloycontaining up to 10% osmium.

2. An X-ray tube, having an anode body with an exposed electron impactsurface, and electron beam means for producing an electron beamimpinging on said surface and causing emission of X-rays therefrom;

said electron impact surface consisting of a tungstenrhenium-osmiumalloy containing up to 25% rhenium, up to 10% osmium and the remainderof tungsten.

3. An X-ray tube, having an anode body with an ex- 3 posed electronimpact surface, and electron beam means for producing an electron beamimpinging on said surface and causing emission of X-rays therefrom;

said electron impact surface consisting of a tungstenrhenium-osmiumalloy containing from 1 to 10% rhenium, .1 to 10% osmium and theremainder of tungsten.

References Cited UNITED STATES PATENTS 3,328,626 6/ 1967 Natter et al75176 X 4 648,660 5/1900 Fessenden 313330 2,863,083 12/1958 Schram313330 3,136,907 6/1964 Kieffer et a1 313-330 X OTHER REFERENCES Journalof the Less Common Metals, vol. 1, 1959, Kieffer et al., February 1959,p. 26.

X-Rays, Kaye, 2nd ed., Pub. by Longmans Green and Co., New York, p. 39.

5/1967 K hl 75.476 X 10 CHARLES N. LOVELL, Primary Examiner.

